Discerning the Role of an A-Site Cation and X-Site Anion for Ion Conductivity Tuning in Hybrid Perovskites by Photoelectrochemical Impedance Spectroscopy

Abstract

Hybrid perovskite materials are mixed electronic–ionic conductors which enhance the complexity of conduction in these materials. Complete understanding of ionic conductivity along with electronic conductivity is crucial. Herein, we employed photoelectrochemical impedance spectroscopy on a perovskite/electrolyte interface-based device to investigate the role of an A-site cation and X-site halide ion in dictating the charge and ionic conductivity of the perovskite material. It was noted that ionic conductivity of the perovskite material can be tuned either by changing the A-site cation (MA+/FA+) or by changing the X-site halide ion (I–/Br–). Photoinduced ionic conductivity can be significantly different (opposite) in different cation perovskites or different halide-based perovskites. Therefore, mixed-cation perovskites can be utilized to reduce photoinduced ion conductivity. Furthermore, very fine tuning is also possible by modulating with the external applied bias. The influence of ion accumulation and migration on the charge storage and transport property of the device is analyzed using vacancy hopping and the jump relaxation model. Ionic conductivity spectra revealed Jonscher’s law dependence in the mid- and low-frequency range with a constant plateau at high frequencies. It can be concluded that the interplay of ion migration and accumulation decides the resulting conduction and storage property of the complete device. These perovskite/electrolyte-based devices can therefore be promising candidates for electrolyte-gated perovskite field-effect transistors where switchable ion conductivity can be achieved either by photoexcitation or external electric field.

Ion Migration in Organic–Inorganic Hybrid Perovskite Solar Cells: Current Understanding and Perspectives

“…[102] In fact, this large capacitance that occurs in the low-frequency (LF) domain is also considered by other works as a way to detect the ion migration and the degree of accumulation at the interface. [103,104] IS works by monitoring the response of the sample to an electric field and as a function of frequency (ω). The complex impedance Z (Ω cm −2 ) is obtained from the relationship between the AC voltage and current response.…”

“…On the basis of the dominant role of ion migration at grain boundaries, it is crucial to suppress ion migration by passivating the defects at grain boundaries. [93][94][95][96][97][98][99][100][101][102][103][104][105][106][107][108][109][110][111][112] Liu et al proposed a strategy to passivate grain boundaries and inhibit ion migration by methimazole (MMI). [113] From the EDS results, it can be seen that the intensity of I in the initial aging device decreased from the HTL side to the ETL side, indicating that I migrated in the perovskite (Figure 9a).…”

“…On the basis of the dominant role of ion migration at grain boundaries, it is crucial to suppress ion migration by passivating the defects at grain boundaries. [ 93–112 ] Liu et al. proposed a strategy to passivate grain boundaries and inhibit ion migration by methimazole (MMI).…”

Recent Development and Directions in Printed Perovskite Solar Cells

“…and R X are the radius of the A-site and B-site cation, and X-site anion, respectively. [23] A stable black phase of the perovskite can be obtained when 0.8 ≤ t ≥ 1 and 0.44 < μ <0.9. [24] However, a perfect cubic symmetry of perovskite requires a t-factor between 0.9 and 1.…”

Terpyridine-derived perovskite single crystals with tunable structures and electronic dimensionality

“…17,18 It is noteworthy that a particularly diverse variety of 0D and 1D perovskites have been made by incorporating organic cations with different sizes inside the Pb-I framework as a result of being able to relax restrictions on the sizes of the cations. [19][20][21][22] The 1D and 1D-2D or 1D-3D halide perovskite materials have recently emerged as a highly promising class of functional materials for a variety of applications. It has been found that deposition of a 1D layer on top of a 3D material can increase the air and heat stabilities of the corresponding device, 23 and that formation of 0D-2D hybrids can simultaneously improve photoresponses and yield higher performance levels in optoelectronic devices.…”